The calibration data were fitted to mixture Poisson models with \(K=2,3,4\)  and 5 components. Based on the Akaike information criterion (AIC [1]}), we found that the best model was the mixture Poisson model with \(K=4\)  components. Moreover, we chose a model where the parameter \(u_{k}\)  is equal in all four components and from now on it will be denoted as \(u\) . It means that for further analysis the mixture Poisson model with 4 components was chosen with mean given by
\(\lambda _k(d,t)= c_k \cdot t^{u} + a_k \cdot t^{v_k} \cdot d, \hspace{28.45274pt} k=1,2,3,4.\) 
